Coulombic efficiency, or charge efficiency is the answer to the OP's question, but it is a subject not often explained or understood. Maine
Sail is the only person I know who would TRY and measure it!!!!
Charge efficiency is different to Charge Acceptance Rate.
Charge Acceptance Rate is the amount of current that a battery will accept at a given voltage and given state of charge. AGMs will accept much more than Trojans or any other FLA. So if a Trojan is accepting 50 amps from a 100 amp charge source and AGM may accept the full 100 amps in the initial boost stage of charging, so that part of the charge cycle will be faster.
Battery Charge efficiency is how much of that current is actually converted to stored Ah. This is the value you have to input into a good battery monitor
to help it more accurately calculate the Ah stored in the battery. A typical default value is 85%. Wet Led Acids can be anywhere from 70-85% and AGMs can be as high as 98%. Battery efficiency is very non-linear, so at 50% State of Charge it may be 95%, but above 85% SoC it may be less than 50% which means witrh every 10Ah charged only 5Ah get stored. This gets worse the closer to 100% SoC you get.
So if you want to store 100Ah in an FLA bank with an 80% efficiency then 125Ah has to be input. (80% of 125 is 100). With an AGM bank at 98% efficiency then only 102Ah has to be input to raise the bank by 10 Ah. That's 23% less Ah needed to raise the bank by 100Ah, so it is charging 23% faster. Lifeline claim 20% faster charge. This happens at all stages of the charge cycle, so even a modest Solar Array will put more Ah into an AGM than an FLA bank.
With AGMs you don't need a high current source to charge faster, but it helps. AGMs high Charge Acceptance Rate means that you can happily put 100 amps into a 100 Ah Lifeline battery, whereas Trojan only recommend 10 amps, so Lifelines
can charger very much faster than Trojans.